Colorimetric and Resolution requirements of cameras

Transcription

1 Colorimetric and Resolution requirements of cameras Alan Roberts ADDENDUM 18 rev.1 : Assessment of, and settings for, Panasonic HVX200 Data for this section is taken from short examinations of two production models of the Panasonic HVX200 camcorder. This is a HDTV camcorder, physically very similar to the standard-definition DVX100, with 3 ⅓ ccds, the manual gives no clue as to the sensor resolutions. The two models under test ran only at 60 Hz (actually 59.94) or 50Hz. It records HDTV using the DVCProHD algorithm onto P2 flash cards (1080i, 1080psf, 720p), SDTV using any of the DVCPro50 or DVCPro or DV algorithms onto P2 cards (480i, 480psf, 480psfa* or 576i, 576psf, 576psfa), and SDTV onto minidv. It can also shoot off-speed when recording 720p onto P2 cards, but only at spot speeds, it is not continuously variable as is the Varicam AJ- HDC27F. The camera is relatively light and has an integral lens and viewfinder, with side lcd panel, and seems aimed at the high-end consumer/professional market rather than full broadcast, which would normally demand interchangeable lenses. It is the first tapeless camcorder for HDTV. It has a photographic speed of about 640ASA. It has the usual internal menus for setting the performance, not as complex as in the 720-line Varicam or the 1080-line HDX400, but enough to control most of the important features. It is not suited to multi-camera operation. It has analogue-only video outputs (components at both HD and SD via a multi-pin connector) and digits via IEEE1394 Firewire and USB. This alone puts the camera in the consumer/semi-pro market, rather than broadcast, which would normally expect either HDSDI or BNC connectors for analogue. The same assessment procedure was used as for other HD cameras, partly attempting to get a good filmlook, and the settings reflect that. It is useful to think of the camera, when used in this way, to be mimicking a film camera and telecine, with best light transfer to tape, with about 10 stops of tonal range. Assuming that a grading operation will be used in post-production, the settings attempt to give the colourist the same range of options as with film. The recommended settings allow about 1.3 stops of over-exposure and one of under-exposure relative to normal operation. This is not as good as can be achieved in 2 /3 cameras, and arises from the difference in pixel size (the pixels here are much smaller, so sensitivity is maintained at the expense of highlight handling and video noise). This revision corrects some minor typographical errors, none of which have any effect on picture or sound quality. 1

2 Colorimetric and Resolution requirements of cameras Alan Roberts ADDENDUM 18 rev.1 : Assessment of, and settings for, Panasonic HVX200 The assessment of this camcorder was aimed mostly at discovering what it could do, rather than deriving a preferred setting, results are given in Section 2. The controls are not as flexible as for full broadcast cameras, so it may or may not be possible to derive a specific film-look for it. However, there is sufficient flexibility to achieve much of what is desirable in film-look settings. Photographic speed is about 640ASA. Many of the menu items have little or no effect on image quality. Those that have significant effect are highlighted. The full set of menu items is given for completeness. In boxes with a range of numeric settings, e.g. -99~99, the values indicate the range, and zero means no alteration to factory setting, not zero effect, and no scales are given. For each item, the factory setting is given if it is known, and the range offered by the camera under test. BBC settings are in the last column, where appropriate. The following table shows the menu settings when the camera is in mode, these affect picture performance; other menus are included for completeness. Values that are underlined are the factory default settings. The menus share some features with the Varicam, in that Scene Files store a great deal of information, permitting widely different settings to be stored. BBC-preferred values are given for SD operation, for 1080 interlaced and psf, and for 720 film and sport (where sport covers all uses that are not intended to look like film). Items that have an important affect on picture appearance are highlighted. Some items are valid only for tape- or P2-operation, all items are flagged. It is unfortunate that the colour bars that the camera generates are only 100/0/75/0 (i.e. EBU) rather than the much more useful SMPTE bars that are ubiquitous in HDTV. This revision corrects some minor typographical errors, none of which have any effect on picture or sound quality. This is not intended as a replacement for reading the manual. 1 Menus and Settings CAMERA MENU SCENE FILE CAMERA SETUP SW MODE AUTO SW RECORDING SETUP AV IN/OUT SETUP DISPLAY SETUP CARD FUNCTIONS OTHER FUNCTIONS OPTION MENU MCR/VCR MENU RECORDING SETUP PLAYBACK FUNCTIONS AV IN/OUT SETUP DISPLAY SETUP OTHER FUNCTIONS OPTION MENU operational controls, needs lab work to get the best from these Basic camera setup controls Configuration of switches Control of camera automatic features Tape and P2 card controls Configure audio/video connections Viewfinder and LCD panel settinmgs P2 flash card controls Sundries that don t fit anywhere else Control of IEEE1394 (Firewire) connection Timecode, IEEE1394, User bits audio, etc Audio matters Analogue connection and IEEE1394 settings Viewfinder and LCD panel settings Sundries that don t fit anywhere else Control of IEEE1394 (Firewire) connection 2

3 DUBBING MODE MENU RECORDING SETUP DUBBING SETUP Timecode, IEEE1394, User bits audio, etc Format, pulldown etc CAMERA MENU SCENE FILE (1-6) mode range comments BBC Operation type (P2, tape) Video/Film Frame rate (P2) 60 12, 18, 20, 22, 24, 26, 30, 32, 36, 48, , 18, 20, 23, 25, 27, 30, 32, 37, 48, 50 Synchro scan (P2,tape) 1/n~1/249.8 Also sets SynchroScan indicator to time or angle Shooting speeds for 720p only n=frame rate, or degrees for FILMCAM, will not set longer than 1/field or frame 0 (1080i) -2 (1080p) +2 (720sport) -4 (720film) Detail level (P2,tape) -7~+7 Horizontal and vertical edge detail V Detail level (P2,tape) -7~+7 Vertical edge detail 0 (SD) -2 (1080i) -4 (1080p) +3 (720sport) 0 (720film) -2 (SD) Detail coring (P2,tape) -2~+7 Noise limiting for detail +4 Chroma level (P2,tape) -7~+7 Saturation 0 Chroma phase (P2,tape) -7~+7 Hue 0 Color temp (P2,tape) -7~+7 Fine white balance offset Master Ped (P2,tape) -15~+15 Master black lift A. Iris level (P2,tape) -4~+4 Auto iris gain News gamma (P2,tape) On/Off Gamma (P2,tape) HDnorm, Low, SDnorm, High, B.press, Cine-likeD, Cine-lineV Adds some extra knee to cope with highlights HDnorm= ITU709, Low=high contrast (skin press), SDnorm=DVX100, High=black stretch, B.press crushes, CineV=more contrast than CineD Off HDnorm (HD), High (SD) Knee (P2,tape) Auto, Low, Mid, High Reaches ~ 250%, knee at 80%,90%, 100% 90% 60 Norm, Enriched, Fluo, Cine-like Norm/ Matrix (P2,tape) Not specifically tested Norm1 50 Norm1, Norm2, Fluo, Cine-like Skin tone detail (P2,tape) On, Off Reduces skin detail Off V Detail freq (P2,tape) Thin, Mid, Thck Thin and Mid may cause twitter Thin Name edit (P2,tape) Names the selected scene file Save/init (P2,tape) Save, Initial Save changes, or factory reset CAMERA SETUP mode range comments BBC Aspect conv (P2,tape) Normal, Letter box, Squeeze Recording format for 480-line Setup (P2) 60 0%, 7.5% Composite black level for NTSC output Setup (tape) 60 0%, 7.5% Composite black level for NTSC output Mid gain (P2,tape) 60 0, 3, 6, 9, 12dB 12dB gain is fairly noisy and visibly soft, 3dB High gain (P2,tape) 60 0, 3, 6, 9, 12dB probably not acceptable 6dB ATW (P2,tape) 60 Ach, Bch, Prst, Off Assign AutoTrackWhite to gain switch Handle zoom (P2,tape) 60 L/Off/H, L/M/H, L/OFF/M Set zoom speed switch settings, Iris dial (P2,tape) 60 Down open, Up open Reverses iris control (when Manual) SW MODE mode range comments BBC 3

4 User 1,2,3 (P2,tape) RecCheck, Spotlight, Backlight, Blackfade, Whitefade, ATW, ATWon/off, Gain18dB, FocusRing, IndexMemoP2, SlotSelP2, ShotMarkP2 Assign user switches. 18dB works only with 60Hz formats, and not with slow shutter. P2 options label shots, change slots etc. Default:1=Whitefade, 2=Backlight, 3=Index/Memo AUTO SW mode range comments BBC A.Iris (P2,tape) On, Off Auto iris AGC (P2,tape) 6dB, 12dB, Off Set auto gain maximum ATW (P2,tape) On, Off AutoTrackWhite AF (P2,tape) On, Off AutoFocus, disables Focus/Push Auto RECORDING SETUP Rec format (P2) Rec format (tape) mode range comments BBC 480i rec mode (P2) 576i rec mode (P2) 50 Rec function (P2) One-shot time (P2) Interval time (P2) 1080i/60i, 1080i/30p, 1080i/24p, 1080i/24pa 1, 720p/60, 720p/30, 720p/24, p/30pn 2, 720p/24pn, 480i/60i, 480i/30p, 480i/24p, 480i,24pa 1080i/50i, 1080i/250, 720p/50p, 720p/250, p/25pn, 576i/50i, 576i,25p o/60i, 480i/30p, 480i/24p, 480i/24pa i/50i, 576i/ DVCPro50, DVCPro, DV Normal, Interval, One shot, Loop 1F, 2F, 4F, 8F, 16F, 1s 2F,4F,8F,16F, 1s, 2s, 5s, 10s, 30s, 1m, 5m, 10m 4 Recording format for P2 card, this terminology is nonstandard, but the meaning is clear. Tape recording format Tape compression system Non-standard recording functions Frames or time to record Frames/seconds/minutes Prerec mode (P2) On, Off Memory cache for prerecording Rec speed (tape) Vcr/Dub SP, LP Tape speed Audio rec (tape), Vcr 32k12bit, 48k/16bit The usual Mic alc (P2/tape) On, Off Auto level control Mic gain 1 (P2/tape) -50dB, -60dB External mic level control Mic gain 2 (P2/tape) -50dB, -60dB External mic level control 25M rec ch sel (P2) 2ch, 4ch DV/DVCPro25 sound channels 1394 TC regen (P2/tape) On, Off On=TC from 1394, Off=other controls TC mode (P2/tape) TCG (P2/tape) First rec TC (tape) TC preset (P2/tape) / Dub / Dub Vcr/ Dub / Dub 60 DF, NDF Free run, Rec run Regen, Preset Only relevant in the 59.94Hz variant, 24p uses NDF TC runs free or only when tape runs Select TC used at start, Regen reads tape and continues Set initial TC, when recording 24p, set frame to multiple of 5 for it to make sense 1 psfa is the slightly improved variant of the 2:3 pulldown process used to derived 60 fields from 24 frames. Conventionally, 2 fields are made from one frame, then 3 fields from the next; this results in video frames grouped in sequences of 5, only two of which contains only information from one source frame, the others contain information from 2 source frames. In this variant, the pulldown sequence is 2:3:3:2, such that only 1 video frame in a group of 5 contains information from 2 source frames. This solves many problem in production and distribution, while somewhat attenuating the uneven progress of motion caused by the 2:3 process. 2 pn mode records only new frames, for over/undercranking, i.e. there is no frame repetition.

5 1394 UB regen (P2/tape) On, Off Source of UserBits UB mode (P2/tape) User, Time, Date, TCG, FrmRate / Dub FrameRate uses a code, refer to manual UB preset (P2/tape) / Dub Set info, select User in UB mode 1394 In preset (P2/tape) On, Off Sync TCG to 1394 when TCSet pressed PLAYBACK FUNCTIONS mode range comments BBC 32k audio (tape) Vcr ST1, ST2, Mix Route stereo 1/2 or 3/4 to output when 32k Audio out (P2) Ch1Ch2, Ch1, Ch2, Channels 3 and 4 available only on P2 Mcr.Vcr Audio out (tape) Ch3Ch4, Ch3, Ch4 recording PLAYBACK FUNCTIONS Format sel (P2) Dub 60 mode 60 range comments BBC 1080i/60i, 1080i/30p, 1080i/24p, 1080i/24pa, 720p/60p, 720p/30p, 720p/24p, 720p30pn, 720p/24pn 5 Clip format for dub playback Pulldown sel (tape) Dub 60 24p, 24pa 23 or 2332 pulldown to 60 Setup (tape) Dub 60 0%, 7.5% Composite setup for NTSC DUBBING SETUP mode 50 range comments BBC Format sel (P2) Dub i/50i, 1080i/25p, 720p/50p, 720p/25p, Clip format for dub playback 720p/25pn Pulldown sel Dub 60 24p, 24pa 2:3 or 2:3:3:2 pulldown Setup Dub 60 0%, 7.5% AV IN/OUT SETUP mode range comments BBC Cmpnt out sel (P2) Mcr 720p, 1080i, 480i 720p converts only to 1080i HP mode (P2,tape) Live, Recording Headphone feed, use Live for off-speed A.dub input (tape) Vcr Mic, A.In Take sound from mics or audio I/O 1394 out (tape) Vcr On, Off On feeds analogue inputs to 1394, adc DISPLAY SETUP mode range comments BBC Zebra detect 1 (P2,tape) 50%~105% by 5% Default 80%, left-leaning zebra Zebra detect 2 (P2,tape) 50%~105% by 5%, Off Default 100%, right-leaning zebra Marker (P2,tape) On, Off Press Zebra button to display markers Safety zone (P2,tape) Off, 90%, 4:3 Video out OSD (P2,tape) On, Off Screen info to video output, beware, it goes to 1394 as well Date/Time (P2,tape) Level meter (P2,tape) Zoom, focus (P2,tape) Off, Time, Date, Time&Date On, Off Off, Number, mm/feet, mm/mm What to show on screen Audio levels on screen Show real distances (maybe ) Card/Tape, Batt (P2,tape) On, Off Remaining capacity Other display (P2,tape) Off, Partial, All Display info depth data (P2,tape) On, Off Show camera settings on playback LCD backlight (P2,tape) High, Normal Brightness LCD set (P2,tape) Panel, set brightness, contrast, colour

6 EVF set (P2,tape) V/F, set brightness, contrast, colour Self shoot (P2,tape) Normal, Mirror For when panel is forward-facing EVF mode (P2,tape) On, Auto Auto switches off V/F when panel is open Display aspect (P2,tape) Auto, 4:3 Widescreen always appears letterboxed EVF color (P2,tape) On, Off For black/white V/F CARD FUNCTIONS mode range comments BBC Scene file (P2) Read, Write Save up to 4 scene files to P2 card User file (P2) Read, Write Save up to 4 file settings (not Scene) to SD card SD card format OTHER FUNCTIONS Remote (P2,tape) mode range comments BBC Mcr,Vcr Vcr1, Vcr2, Off 1394 control (P2,tape) Off, Ext, Both Chain Remote control access Backup via 1394, Ext controls remote deck with Start/Stop, Chain uses remote deck as extra recorder 1394 cmd sel (P2,tape) Vcr RecP, Stop Set remote deck to stop or pause End search (tape) Mcr Blank, Rec End Search for unrecorded slot or last recording PC mode (P2) USB device, 1394 Mcr device, 1394 host 1394 host controls external deck for backup Rec lamp (P2,tape) Off, Front, Rear, Both Access led (P2) Mcr On, Off Card access indicator Beep sound (P2,tape) On, Off Warns of card/tape full, no tape, condensation, problem Clock set (P2,tape) Set clock and calendar. Really, honest, that s what it does Time zone (P2,tape) -12~+13 Time zone offset from GMT, for foreigners Power Save (P2,tape) On, Off Disables 5-minute inactive shut-down Language (P2,tape) English, Japanese Menu language, use with care User file (P2,tape) Mcr,Vcr Load, Save, Initial Power down/up to activate change Hour meter Vcr Shows head hours (5 digits per hour) Press Disp/Mode Chk button and Menu, then Menu to cancel OPTION MENU mode range comments BBC 1394 status (P2,tape) 1394 config (P2) Mcr Dflt, 1~255 P2: Format, rate, 50/60, channels, speed, status, video, audio Tape: Format, rate, 50/60, channels, speed, mode, Rx, Tx 1394 extended menus 6

7 2 Measurement results The HVX200 has no built-in test signal generator. This alone sets it apart from most professional and broadcast cameras. Thus all measurements had to be made the hard way, using optical test cards and an awful lot of data processing. Only the 50Hz version was measured in detail, serial number C6TC0015-R. 2.1 Transfer characteristic (gamma-correction) Measurements were made to determine the equations of two of the gamma-correction curves, which also revealed the nominal exposure range of the camera. A Macbeth (Fig.1) chart was evenly illuminated, and recordings made at the full range of exposures. The bottom row of colour patches on the chart forms a grey scale, and the optical density of each patch is given in the specifications of the card, thus it was possible to obtain a large number of measurement points to form a point-wise plot of the gammacorrection curves. Since the iris control is continuous, it was not possible to set exposure precisely for each exposure, nevertheless, judicious adjustments in the data processing has provided a reasonable data set from which to estimate the gammacorrection 1.1 curves. Fig. 2 shows data points for the Hdnorm curve (supposed to be the ITU.709 curve) with Knee set to Mid (which is supposed to break at 90% voltage). It is relatively easy to fit a curve to these points, but it is not easy to be accurate since there is clearly some inconsistency in the data, caused by video noise, slightly uneven illumination, lens vignetting when fully open, imprecise setting of the iris, and so on. The ITU.709 curve, the standard for all HDTV cameras is: The found equations for the Hdnorm curve are: V 4. 5L for L<0.018, else V L^ V 4. 5L for L<0.03, else V 1.05L^ This is a reasonable match to ITU709, but is not perfect. The Knee causes the curve to break at signal levels of 80% (Low), 90% (Mid), 100% (High) and then extend to and exposure limit of 2.5 (250%) before clipping occurs at about 107%. The contrast range for these settings is derived from the equations. The maximum exposure the camera can handle is 250%, while the minimum exposure that is visible in the output can be defined as that which causes the signal voltage to be 2% of the coding range (the video level of the super-black bar in SMPTE colour bars, used for setting display black level). If the noise is low, then a lower point can be taken, 1% would be the normal minimum considered relevant. For the Hdnorm curve, these ratios are approximately 550:1 (9.1 stops) and 1100:1 (10.1 stops), not bad for a camera in this category. Measurements of the High (Black Stretched) gamma-correction curve were surprising, the found equations are: V 5L for L<0.02, else V 1.25L^ Figure 1, Macbeth chart Figure 2, HDnorm gamma, Knee=Mid

8 However, the numbers in this equation are a little extreme, so in a second search a rather better match to the data was found by fitting the BBC 0.4 law to it: for L< , else V L ^0. 4 V 5L Both these curves fit the data well, but the BBC curve (which was designed for SDTV use) seems more natural, and is presumably intended to be so. This gamma-correction curve generally produces more accurate colour rendering. Fig. 3 shows the colour accuracy of the camera using the Hdnorm curve; each colour is shown as a blob where it should be and a cross where the camera produces it. There are significant saturation and hue errors, most significantly in skin tones. The user should generally choose one of these two curves for working in HDTV, Hdnorm produces more vivid colouring while High is more accurate. For normal use, Knee can be set to Auto, but when the production will be going to a colour grading operation, Knee should be set either to Mid or Low, depending on the type of programme (Mid for programmes where skin tone is prevalent, Low for natural-history). The other variants of the gamma curve were not Figure 3, chromaticity of HDnorm curve investigated, the descriptions given in the manual seem to be sufficiently accurate and explicit for the user to make an intelligent choice. 2.2 Resolution and Detail The HVX200 is interesting in that the sensors are not native-sized for HDTV. The 3 ccds are each 960 by 540 pixels; it would be more usual to find sensors, in a 1080-line camera, having 1080 lines rather than only 540. Panasonic chose to use these lower-resolution sensors in order to increase sensitivity (since the pixels are bigger, the same 5µm square dimension as is found in ⅔ format HDTV cameras. The camera delivers HDTV resolutions by physically offsetting the G sensor from R and B by a half-pixel both horizontally and vertically. It is normal to offset just horizontally, when the delivered horizontal resolution is apparently about 50% higher than would be dictated by the pixel count alone. This quincunx offset increases both horizontal and vertical resolution, just how well can only be judged by measurement. This particularly relevant since the camera delivers signals at 1080, 720 and SDTV (both 576 and 480 lines in the two variants). A zone plate test chart was used, calibrated for 1920x1080 HDTV. It contains 6 identical circular patterns, each being a phase space of the spatial-frequencies which such a camera should resolve. Analysis was made of one zone to investigate the frequency responses and the presence of aliases Detail enhancement However, a broad pulse (also on the zone plate test chart) was used for establishing reasonable detail settings, since the function of the detail enhancement is to sharpen edges rather than establish flat frequency responses. Fig.4 shows the effect of setting Detail Level to 0 and 2, there was no setting at which the overshoots were absent, and insufficient other controls to alter the Figure 4, 1080-line pulse response 8

9 way the enhancement works. Judging by eye, setting level 2 seemed reasonable Resolution (1080-line) Fig.5 shows a quarter of one circular zone plate, with zerofrequency at bottom left. The right-hand extreme is 1920 lines/picture width, the top extreme is 1080 lines/picture height. The alias patterns are clear, and indicate that the camera does not deliver full resolution at 1080, either horizontally or vertically. However, it is reasonably well behaved, in that there do not appear to be significant aliases centred on other frequencies, as would be expected if the interpolation process from the 960x540 of the ccds were compromised in any way. The precision-offset of the sensors in cameras is normally only horizontal, which delivers approximately 50% more horizontal resolution than the pixel-count, but with sensors in quincunx arrangement both horizontal and vertical resolutions are increased, but how well and by how much is debatable. The strength of the existing aliases mean that it is difficult to measure the frequency responses accurately, since the higher frequencies are mixed with aliases. Nevertheless, it was possible to extract sufficient data using a software analysis program, to derive both horizontal and vertical frequency responses, and these reveal some interesting information. Figs.6 and 7 show the horizontal and vertical responses for 1080i/25p (usually known as 1080psf/25, film style). It is difficult to decide how to present the amplitudes at greater than 960 horizontal and 540 vertical. It is clear that aliases (unwanted) are present, but so is content at baseband (wanted) frequencies. Since the recording format has a horizontal limit of 1440, not 1920, horizontal frequency content above 1440 must be only alias, there can be no baseband content. In both figures, the green curve shows the response when both Detail Level and Vertical Detail are set to 0, the default value. Clearly, the designers have realised that it is more dangerous to have excess vertical detail over horizontal, but both curves seem excessively boosted at low/mid frequencies; it is in these low/mid frequencies that detail must be well controlled in order to generate a decent film-look, neither of these curves will do. To show how difficult it is to interpret the available measurements, Fig.8 shows the sequence of sample levels in a horizontal scan. The settings given in Section 1 are not ideal; they are subjectively a reasonable compromise, but overall performance of the camera is not a good match to other HDTV cameras in this respect. Figure 5, quarter zone plate, 1080psf/25, detail=-2, v.detail=-4 Figure 6 and 7, horizontal and vertical responses, 1080psf Figure 8, horizontal waveform Resolution (576-line) 9

10 Again, interpretation of data is difficult, but the subjective appearance of resolution is reasonable. Fig.9 shows the horizontal frequency response. The bandwidth is well filled to the 720-pixel limit (perhaps too well filled), but there are significant aliases between 720 and 1440, and the frequencies between 1440 and 1920 show strongly because they are twice-folded. Evidently the Detail controls apply only detailboosting (some HDTV cameras have detail controls that allow detail reduction as well as boosting). For SDTV use boosting is largely unnecessary, so a very low setting is reasonable, in Fig.9 the Detail setting level is 0, and is clearly too much. Judging by eye, a setting level of 2 is the maximum that should be used, and 4 looks better although the picture then starts to look soft because the boosting is done at too Figure 9, horizontal response low a frequency even in the Thin setting. The settings in the table produce pictures that look sharp at the expense of some visible boundary enhancement. The same does not hold for the vertical response, Fig.10, the response falls nicely to zero between 288 and 576, resulting in a moderate amount of interline twitter. The complete lack of vertical aliases at higher frequencies is good evidence that the camera can be used to shoot SDTV pictures, provided Detail is set sufficiently low Resolution (720-line) At the time of testing, it was not possible to analyse single frames of P2 recording, however the visual appearance was a good intermediate between 1080 and 576. The Detail settings in the table are visually appropriate for film- and sport-style shooting, where the film version uses minimal boosting although there is no setting that gets satisfactorily close to a real film-look. The sport version is appropriate for news, sports, any genre other than film-look. 2.3 Noise Figure 10, vertical response No calibrated noise meter was available during the measurement procedure, and the camera specification does not mention noise. Again, software analysis of frames gives some indication of performance. Measuring the signal-to-noise ratio is just one colour patch of the Macbeth chart (the white patch when slightly under-exposed, 0db Gain) gives a figure of 44dB. Although it is highly dangerous to use such a small number of samples for analysis, the error is known to be less than 2dB, thus noise is between 42dB and 46dB. This agrees with subjective evaluation, and explains the high value set for Detail Coring. At +12dB, the noise is plainly visible; even with Detail Coring set to +4, the noise level was sufficiently high to cause detail enhancement to switch off, resulting in visibly softened pictures. This explains the Gain settings of +3dB and +6dB. 10